1. Field of the Invention
The present invention relates to a high power amplifying device and method and, more particularly, to a device for combining outputs of a plurality of linear power amplifiers and outputting the combined outputs and a method therefor.
2. Description of the Related Art
In general, high power amplifiers (HPAs) have to be included in digital mobile communication systems to amplify and output a transmitting RF signal (TX RF signal). Also, in order to amplify their outputs to a maximum power level, such HPAs typically operate in the vicinity of their saturation region which has non-linear characteristics. However, if more than two carrier waves, i.e., multi-carrier waves, are commonly applied to and amplified by a HPA, the non-linear characteristics near the saturation region introduce unwanted intermodulation distortion signals (IMD) and other forms of signal distortion and/or loss.
Thus, although the input RF signal should be decreased by a number of dB so as to be amplified in the linear region, thereby reducing noise of the intermodulation distortion component, there is a problem in that output power may be lowered. In the case that a linearizer is employed to compensate for the non-linear characteristics near the saturation region of the high power amplifier, it is possible to considerably reduce the intermodulation distortion signal which may be generated upon commonly amplifying the multi-carrier waves in the saturation region. An amplifier which employs a linearizer and the power amplifier, as discussed above, is called as a linear power amplifier (LPA).
Thus, since the intermodulation distortion component, as stated above, causes the deterioration of the quality of the transmission as a noise source, the intermodulation distortion signal of the linear power amplifier used for a mobile communication system, such as a code division multiple access (CDMA) system, is required to be about -45 dBc necessarily in an operation bandpass while about -60 dBc elsewhere, as per a spurious standard. Conventionally, when P.sub.1 dB is output in an A-class linear power amplifier, a third intermodulation distortion signal (3rd IMD) becomes -20 dBc, approximately. Therefore, the output of the linear power amplifier should be reduced by about 20 dBc to obtain the intermodulation distortion signal of about -60 dBc in the above A-class linear power amplifier. Also, when the multi-carrier waves are input thereto, the output thereof should be again reduced by about 80 dBc in consideration of the peak value of the output thereof. That is, the A-class linear power amplifier of rated output 12 watts is required to provide an average output of about 20 watts. Since reducing the output of an A-class linear power amplifier is difficult to do, it is generally desirous to provide a linear power amplifier having given linear characteristics by employing a linearizer with an AB-class linear power amplifier having good power efficiency.
At this time, the linear power amplifier used for the above digital mobile communication systems requires that the high power amplifier have a very high output. Accordingly, there is generally known a conventional method to combine outputs of a plurality of low power linear power amplifiers in order to amplify the RF signal to a desired output level. Such a power combining method is disclosed in "Planar Electrically Symmetric n-way Hybrid Power Dividers/ Combiners" (IEEE Transactions on Microwave Theory and Techniques, vol, MTT-28, No. 6, June 1980, pp.555-563).
In such a conventional combining method, an n-Way Winkinson-Type Combiner and an n-Way Radial-Type Combiner are exemplary of an n-way RF power combiner. Hereinabove, the n-Way Winkinson-Type Combiner is constructed with .lambda..sub.0 /4 transmission path and resistors and the n-Way Radial-Type Combiner is constructed with .lambda..sub.0 /2.about..lambda..sub.0 /4 transmission paths.
In the event that the above n-way RF power combiners combine n power supply sources having the same characteristics in amplitude and in phase as each other, the output power is reduced as much as the number of abnormally operating (failed) power amplifiers. In other words, when a failed or abnormal state occurs in m power amplifiers in a high power amplifier using n power amplifiers (where m is less than n), the power amplifying signal combined and outputted is proportional in size to the number of failed power amplifiers. And, the greater the number of the failed amplifiers that occur, the more the output power of -20 log(1-m/n)dB is reduced. In such a case, n denotes the number of the power amplifiers and m denotes the number of failed power amplifiers. Upon the failed state being generated in even one power amplifier of an RF amplifier having a small number of power amplifiers disposed to combine the power, such RF amplifier has difficulty in achieving its objective amplifying efficiency. Thus, there is a problem in that the above-identified amplifier disadvantageously becomes a very inefficient power combiner. As a result, in the event that the high power RF amplifier is constructed with low power RF amplifiers, as stated previously, the above RF amplifier has to have no failed amplifiers.
Likewise, when it is desirable to combine the outputs of the n linear amplifiers by utilizing the above-mentioned n-way power amplifier, the power of the received RF signal is divided by n, the divided n RF signals are amplified through the n linear power amplifiers, and the amplified signals are again combined and outputted. At this time, when an abnormal (failed) state occurs in any particular linear power amplifier forming the power combiner, such single failed amplifier negatively affects the overall output of the power combiner. Further, such failure also negatively affects the overall output of the transmitter. Accordingly, it would be desirable and advantageous to be able to sense the state of the linear power amplifiers before amplifying operation in order to detect a failed condition in any of such amplifiers.